Shaping machine with servo-assisted forming tool

ABSTRACT

The invention relates to a shaping machine with two forming tools pressed against each other, one of which receives from a motor an assisting torque which is proportional to the external force applied to the part to be shaped in order to pass it through the machine. This force is evaluated by feelers which measure the small displacements it imparts to movable bearings which carry the assisted forming tool shaft and are supported on ball-bearings, or to a deformable grip fixed temporarily to the part to be shaped.

[ Mar. 4, 1975 1 SHAPING MACHINE WITH SERVO-ASSISTED FORMING TOOL [75] Inventor: g gg g i gtg gg semourens Primary Examiner-Milton S. Mehr Attorney, Agent, or Firm-Murray Schaffer e "c 8 .I un mm rr n, .5 r 8 8P mn h I a aw .w r 6 SA e n g 9 s A 3 1.

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The invention relates to a shaping machine with two forming tools pressed against each other, one of which receives from a motor an assisting torque which is proportional to the external force applied to the part to be shaped in order to pass it through the machine. This force is evaluated by feelers which measure the small displacements it imparts to movable bearings which carry the assisted forming tool shaft and are supported on ball-bearings, or to a deformable grip fixed temporarily to the part to be shaped.

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UNITED STATES PATENTS 7 I21 17 Claims, 8 Drawing Figures 3.018676 1/1962 Polakowski.............................

PATENTED MAR 4197s saw 3 n 5 SHAPING MACHINE WITH SERVO-ASSISTED FORMING TOOL BACKGROUND OF THE INVENTION The present invention relates to shaping machines with forming tools, used to shape sheets or panels of various materials to the contours of given jigs. Such machines find notable application in the fabrication of car body, airframe, or apparatus-housing elements.

The shaping operation consists in forcing the sheet or panel to pass between two forming tools maintained in mutual pressure contact. The pressure exerted for the purpose on the sheet or panel must exceed the yield strength of the material of which the sheet is made in order to cause permanent deformation through elongation of the fibres. In prior art machines, it is the thrust exerted by an operator that moves the workpiece between the forming tools, thereby causing the same to rotate and the deformation to be propagated.

The thrust exerted by the operator increases with the pressing force between the forming tools. Entrainment between commonly employed forming tools becomes increasingly difficult and even impossible when the pressing force reaches 3 to 4 tons for example, since the extent to which the material has to be crushed be comes too great to enable the workpiece to be displaced by mere manual thrusting.

On the other hand, such pressures are necessary in order to obtain extensive deformation of thick items such as integral-structural aircraft panels.

In the current state of the art, this drawback is overcome by resorting to a plurality of passes each made at maximum possible pressure. However, this results in strain hardening of the work surface and requires subsequent heat treatment before shaping can be resumed. Yet it is not always possible to carry out such treatment, in which case the shaping of certain items becomes impossible; when such treatment is possible, however, shaping operations take a long time.

The object of the present invention is to facilitate shaping operations and to permit time saving in the case of shaping machines utilizing forming tools, of the kind hereinbefore described, making it possible to shape panels under a pressure of between 2 and 10 tons, using ordinary forming tools, with no particular force exerted by the operator, and with a single pass through the machine.

SUMMARY OF THE INVENTION This invention accordingly relates to a machine having two forming tools, one of which is rotated by a motor which exerts torque as a function of the thrust exerted by the operator on the workpiece. In this mannor, said motor assists the operators action, whereby the thrusting force which he must furnish is greatly decreased.

ln one specific embodiment of the invention, the operators thrust can be evaluated because the forming tool haft connected to said motor is not fixedly supported but is able in particular to revolve about another shaft parallel to it. Accordingly, a thrust exerted by the operator produces a displacement of the tool shaft, for instance a revolving thereof about said other shaft the amplitude and direction of which are measured in order to proportionately adjust the assisting torque applied by the motor to the forming tool. The bearings supporting the rotatable shaft of the assisted forming tool are carried eccentrically on auxiliary bearings. One at least of these latter bearings may be a hydrostatic bearing having divided supporting pockets. The hydraulic pressure is measured in certain of these pockets, and this measured value is used to control the motor driving the servo-assisted forming tool.

The pressure exerted on the forming tools by the operator when he inserts the item to be shaped between them, or when he pushes or pulls it after inserting it, produces a difference between the internal pressures in the supporting pockets. Pressure sensors are placed in these pockets and the signals which they deliver are compared in a circuit which in turn delivers a difference signal together with its algebraic sign. This signal is then used to control the extent of the torque applied to the forming .tool by the servo-motor.

Such a device for evaluating the external force exerted is highly sensitive and requires an extremely rigid stand, since the slightest change in position in the alignment of the component parts (and in particular the slightest defect of parallelism between the forming tool shafts) will flaw the force measurement and make the servo-assistance incoherent.

Now in certain cases it is not possible to mount the forming tool supports on a very rigid stand through lack of space or because of the size of the items to be shaped. In order to enable a shaping machine with servo-assisted forming tool to be used even though its supporting stand may have inadequate rigidity, the sensitivity of the device for evaluating the external force applied to the workpiece must be reduced.

In a preferred embodiment of this invention, the hydrostatic auxiliary bearings carrying the movable bearings of the servo-assisted forming tool are accordingly replaced by auxiliary bearings of fixed geometrical structure such as ballor needle-bearings, and the angular displacements of these bearings responsively to the externally applied forces are measured by fixed force sensors such as piezoelectric gauges connected to one of the auxiliary bearings through a flexible vane.

An alternative embodiment of the invention for achieving the same end consists in providing the item to be shaped with at least one manual grip fixed to it temporarily and capable of being deformed, by bending or through articulations, responsively to the external forces applied to the workpiece through said grip, .the latter being associated to displacement sensing means for measuring the corresponding deformations.

In such cases it is unnecessary to provide auxiliary bearings for the assisted forming tool. Should the machine have such bearings, they can be immobilized or even eliminated, the shaft of the assisted forming tool then rotating directly in a fixed support.

The latter-mentioned two forms of embodiment provide diminished sensitivity in measurement of the forces applied to the workpiece, such measurements being then made over a wide range and more independently of rigidity imperfections in the supporting structure of the shaping machine in question.

The description which follows with reference to the accompanying non-limitative exemplary drawings will give a clear understanding of how the invention can be carried into practice.

BRIEF DESCRIPTION OF THE DRAWING In the drawings:

FIG. 1 is a perspective diagrammatic portrayal of one of the forming tools of a machine according to this invention, and the manner of its fitting thereto;

FIG. 2 shows diagrammatically in side elevation the two forming tools of the machine;

FIG. 3 is a plan view, in fragmental section, ofa forming-tool hydrostatic bearing;

FIG. 4 is a perspective view of a complete machine according to this invention;

FIG. 5 is a schematic electric circuit diagram for controlling the servo-motor;

FIG. 6 is a view corresponding to that of FIG. 4 showing an alternative form of embodiment of the invention; and

FIGS. 7 and 8 show two possible embodiments of a grip according to this invention and its manner of temporary attachment to the workpiece.

DESCRIPTION OF THE INVENTION Essentially, a shaping machine according to this invention includes two roll-shaped forming tools 1 and 2 of different diameters and parallel shafts, between which an item 3 to be shaped, such as sheet material or a panel, is inserted and powerfully compressed in order to impart thereto a permanent set or deformation. To that end, the forming tools are urged against each other by a force F which may attain about ten tons and which tends to move their respective shafts 4 and 5 closer together.

Insertion of workpiece 3 with sufficient force causes forming rolls 1 and 2 to rotate about their axes and to ingest the workpiece. In order to decrease the insertion force required, which may be considerable if the crushing force F applied by the rolls on the workpiece is very great, shaft 4 of roll 1 is connected to a motor 6 capable of rotating roll 1 about the axis 14 of its shaft 4 in the direction corresponding to the desired direction of travel of workpiece 3, by applying to it a torque which must be a function of the magnitude and direction of the thrustf applied to the workpiece.

Whereas shaft 5 of forming roll 2 rotates directly between the arms of a clevis 35, shaft 4 of roll 1 is supported in the hubs of auxiliary bearings 7, 8 having a common geometrical axis 9 and carried in the arms of a clevis 34. In one form of embodiment, the bearings 7 and 8 are hydrostatic bearings and each includes a housing 10 that forms supporting pockets such as 11 and 12 around a cylindrical hub 13 of axis 9. In accordance with this invention, the axis 14 of shaft 4 of roll I and the roll-bearings axis 9 are not one and the same but parallel and spaced by a distance d.

A result of this arrangement and of the particular value imparted to dis that, in the absence of any thrust fon workpiece 3, the system assumes a resting position in stable equilibrium wherein axes 14 and 9 and axis 15 of roll 2 lie in the same plane, with axis 9 located between 14 and 15 and the centre of forming roll 1 lying at 0 (FIG. 1).

If a forcef is now applied to workpiece 3 in order to insert, push or pull it between rolls 1 and 2, then because force f is perpendicular to the plane of the roll axes, axis 14 of articulated roll 1 tends to shift in the direction of force f. This shift produces a slight rotation of hydrostatic bearings 7, 8 about their axis 9, with the centre of roll 1 moving to 0 or 0 along a circle of axis 9 and radius d.

If said bearings comprise two pockets on either side of axis 14, separated by a rib lying in the plane containing axes 14, 15 and 9 when the system is in its rest configuration .in the absence of a force f, then the hydrostatic pressures prevailing in these pockets (which were previously equal in the rest configuration) become different by reason of the slight rotation of bearings 7, 8 and the value of this pressure differential governs the diviation of the system from its rest position. The application by motor 6, to forming roll 1, of an appropriately directed torque proportional to this pressure differential will tend to restore it to its initial position, whereupon said forming roll performs the forming operation on workpiece 3 as a result of the torque imparted by motor 6 rather than the direct thrust f exerted on the item, which thrust may accordingly be very small in magnitude.

Accordingly, if the thrust f persists, the imbalance in the system also persists, as well as the pressure differential between said supporting pockets, and the motor'6 therefore continues to rotate.

If the thrustfceases, roll 1 tends to revert to its rest position, the situation of imbalance disappears, the pressures in the pockets become equal, and the motor consequently stops.

Similarly, should the thrust be reversed, the imbalance is also reversed and the motor drives the item to be shaped in the opposite direction.

Accordingly, the desired travel motion of workpiece 3 between rolls 1 and 2 receives servo-assistance from motor 6, the role of the externally applied force fbeing confined to initiating each travel motion, and the power required to perform the shaping being supplied by the motor. The workpiece can thus be inserted, pushed or pulled between the forming rolls with only very small force if and when the compression force F is high.

In practice, each pocket 11, 12 is supplied with hydraulic fluid through a calibrated jet 21, 22. In the rest configuration, a pressure p prevails in the pocket such that the flow rate through the jet resulting from differences between the feed pressure P and the internal pressure p is equal to the leakage flow rate 1 This leakage depends on the clearancej and the pressure p.

The bearing force from each pocket is equal to Sp, where S is the area which the pocket offers to the hub.

When there is a state of equilibrium in the resting configuration under the compression force F exerted by roll 2, the following obtains in each pocket:

assuming that only one of the bearings 7, 8 absorbs the load exerted by roll 2.

As soon as the operator exerts a thrust f on workpiece 3, the direction of the resultant of the forces exerted on roll 1 is no longer vertical and tends to shift the forming roll in the direction of the force exerted. This in turn tends to reduce the clearance j of the pocket located in the downstream direction of thrust, to the detriment of the clearance of the upstream pocket. In the case of the latter, since the clearance has increased, the leakage flow q augments and produces greater flow through jet 22, whence a higher pressure loss occurs in that pocket and p becomes p,, with p p. In the case of downstream pocket l1,j, decreases, and consequently also the leakage flow, whereby the pressure loss decreases and p increases t P1, with p p.

As a result of the force exerted by such thrust, a state of equilibrium is established that can be expressed as:

where the vectorsl??? and :95; are parallel to the lines bisecting the angles at the centre of pockets 11 and 12.

Sensors or transducers 31, 32 measure p and p and deliver, through the agency of a differential amplifier 16, to the inputs 53, 54 (to which they are connected), a signal D proportional to (p p,), which signal operates on a servo-valve 17 which controls the rotation of motor 6 to drive forming roll 1.

Servo-valve 17 may be of the electro-hydraulic type, for example, and constitutes a power relay between the differential amplifier and a hydraulic motor 6 which drives the shaft 4 of roll 1 directly and is connected through conduits 18, 19 to servo-valve 17, to which valve fluid under pressure is supplied through a conduit 20.

Alternatively, the signal D can be applied to an electromechanical relay or to a magnetic or electronic amplifler, in which case motor6 is preferably an electric motor.

In cases where the sensitivity of the devices hereinbefore described appears too high because of insufficient rigidity in the supporting mount of the shaping machine, an alternative embodiment of the invention is to be preferred, in which the hydrostatic auxiliary bearings 7, 8 are replaced by fixed-geometry mechanical bearings such as ballor needle-bearings. In this embodiment, shown in FIG. 6, the means for sensing small rotations of mechanical bearings 7, 8 consist of a flexible vane 50 acting on two force sensors 51, 52. Flexible vane 50 has one of its ends fixed to the hub of auxiliary bearing 7 by means of a bracket. The vane is an elastic blade arranged radially with respect to auxiliarybearings axis 9 and able to flex in a plane perpendicular thereto.

Positioned on either side of the other end of the vane, in contact with the sides thereof, are two piezoelectric force sensors 51, 52 such as quartz crystal gauges made fast with clevis 34. One contact plate of each gauge is earthed on amplifier 16 in the activation chain for motor 6 (FIG. 2), the other contact plate being electrically connected to one of the two differential inputs 53, 54 of amplifier 16.

The voltages delivered by gauges 51, 52 will depend on the magnitude and direction of the urging forcefapplied to workpiece 3. Through the medium of differential amplifier 16, these voltages produce a signal D which operates on servo-valve 17 controlling the motor 6 for driving forming roll 1.

Gauges 51 and 52 perform the same function as the previously described pressure sensors positioned in some of the bearing pockets of the hydrostatic auxiliary bearings, but in this case with enhanced sensitivity and over a wider measurement range that is easier to determine by adjusting the length and flexibility of vane 50.

Alternatively, in accordance with this invention the urging force f may be evaluated, in order to control motor 6, not upon the shaping machine itself but directly in the area of its application to workpiece 3. Accordingly, the end of workpiece 3 has attached thereto a device 36 which comprises at least one actuating grip 39 having a structure such that it is distortable responsively to the force f, together with means for measuring such distortions that are connected, as precedingly described, to the differential inputs 53, 54 in the chain for grip 39, is removable and is fixed to workpiece 3 for the duration of the shaping operation, after which it is removed.

The provisional attachment of device 36 to workpiece 3 may be effected by means of a screw clamp, pressing means, an arrangement of suction cups or electromagnets, or by any other convenient means. In the exemplary embodiment herein described, the device 36 is made ofa hard material, such as metal or reinforced or non-reinforced plastics, and is formed with a rectangular slit 43 through which one end of the workpiece is inserted. This slit makes the device 36 resemble a clevis between the arms of which the said end of the workpiece is clamped by a plurality of elements such as, say, two terminal pressure screws 38. These screws engage into holes tapped into one of the arms of the clevis formed by device 36. Subsequent to clamping, the screws 38 exert their pressure on the workpiece through a backplate 37.

In one form of embodiment (FIG. 7), there is fixed to one side of the device 36 a grip made up of two parts 39, 40, the part 39 being longer than the part 40 having a degree of flexibility such that the gap 41 between the extremeties of parts 39 and 40 varies when force is exerted on part 39 in one direction or the other. Positioned within this gap 41 separating the mutually facing parts 39 and 40 is a displacement detector 55, such as a double-acting piezoelectric quartz-blade gauge which is installed precompressed to an extend slightly greater than the anticipated pulling forces (forces tending to open the grip). The middle plate of the gauge is earthed to amplifier 16 and the terminals 63, 64 of the end plates are connected respectively to amplifier inputs 53, 54. It is possible to combine an alternating-current voltage with the direct-current voltages delivered by gauge 55, in which case the peak to-peak amplitude of the signal will not vary but the signal itself will shift in relation to the earth point. The frequency of such a signal may be 400 Hz for instance. The signal for controlling servo-valve 17 is detected at the inputs to amplifier 16.

Alternatively, the gap 41 may be left free and two strain gauges 42 may be attached, by bonding say, on either side of grip portion 39, not far from its point of attachment to device 36. These gauges measure the force f transmitted by the grip. The two gauges have an end each thereof interconnected and earthed on amplifier 16, the other two ends 73, 74 being connected to inputs 53, 54 respectively of amplifier 16, said inputs being appropriately polarized by means of an auxiliary d-c or a-c voltage.

In accordance with another alternative embodiment (FIG. 8), the grip 39 is hingedly connected to a pivot 44 fast with the device 36, is other end being hingedly connected at 49 to a rod 47 fast with the slide 45 of a potentiometer 46. Slide 45 is electrically connected through a flexible lead 60 to the earth point of amplifier 16, and the ends 83, 84 of potentiometer 46 are connacted as previously described to the appropriately polarized inputs of amplifier 16. Two coil springs 48 are maintained slightly compressed when inoperative, respectively between two flanges 56 fast with the rod 47 and a wall 58 of device 36 which is formed with a recess 57 in this particular embodiment. An opening 59 formed in said wall allows rod 47 to extend therethrough, but not the springs 48 which, when the grip is manipulated, provide the operator with a sensation of muscular feel and thereby enable the displacement of potentiometer slide 45 and hence control over the servo-assisted forming roll to be weighted. When a force f is applied to grip 39, the latter pivots and causes slide 45 of potentiometer 46 to shift. Amplifier inputs 53, 54 are accordingly unbalanced proportionately with respect to earth, and the amplifier output provides a signal D which is proportional to the force f applied to grip 39 and which is polarized according to the direction in which this force acts.

In the embodiments illustrated in FIGS. 7 and 8, the device 36 may be fitted with two grips, only one of which is deformable and equipped with means for measuring the force fapplied by an operator to workpiece 3, the other grip being used to guide the workpiece between forming rolls 1 and 2 to enable it to move laterally during shaping operations. Furthermore, it is no longer necessary for the axis 14 of servo-assisted roll 1 to be translatable parallel to itself. If grips are used with a machine which is equipped with hydrostatic or mechanical auxiliary bearings, the hubs of such auxiliary bearings are fixedly restrained by any convenient means such as screws, points, or plates for rigidly uniting the outer portions of the hubs with the clevis 34. Alternatively, recourse may be had to a machine devoid of such auxiliary bearings, in which the shaft 4 of the servo-assisted roll is carried in bearings housed directly in the arms of clevis 34.

What is claimed is:

l. A shaping machine comprising two rotatable forming rolls with parallel axes between which items to be shaped such as sheet metal or panels are inserted and moved by a force external to the machine, said forming rolls being pressed against each other by a force which subjects the workpiece therebetween to a strain from which ensues a shaping thereof, at least one of said two forming rolls being mechanically connected to a motor associated with regulating means, said motor imparting to said forming roll a torque the magnitude of which is a direct function of the external force applied to the workpiece, said regulating means including an amplification chain comprising a power amplifier that energizes the motor as a function of the output signal from a differential ampltier across the inputs of which is connected a sensing device for measuring the magnitude and direction of the external force applied to the workpiece, shaping means in which a forming-roll shaft connected to said motor rotates in movable bearings which effect small displacements, the magnitude and direction of which are measured by the sensing device and as a result of which the forming-roll axis accompanies the motions of the workpiece in response to the external force, said bearings moving away in such cases from a resting position in which the plane containing the forming-roll axes is parallel to the direction of the force which presses said forming rolls against each other.

2. A machine as claimed in claim 1, in which the slight motions of the movable bearings are rotations about an axis distinct from and parallel to the axis of the forming-roll supported by said 'movable bearings.

3. A machine as claimed in claim 2, in which each movable bearing is eccentrically supported in a circular hub rotating in a fixed auxiliary bearing.

4. A machine as claimed in claim 3, in which the fixed bearings are hydrostatic bearings.

5. A machine as claimed in claim 4, in which each hydrostatic bearing comprises at least two supporting pockets separated by a rib which lies in the plane containing the forming-roll axes in said resting position.

6. A machine as claimed in claim 5, in which the sensing device includes at least one pressure sensor associated to at least one of said supporting pockets whereby to measure the hydraulic pressure therein.

7. A machine as claimed in claim 6, in which the differential amplifier in the amplification chain has its inputs connected to two pressure sensors of a hydrostatic bearing and applies to the power amplifier for energizing the motor a signal proportional to the pressure differential across the corresponding supporting pockets.

8. A machine as claimed in claim 3, in which said auxiliary bearings are bearings with a fixed geometrical structure and the sensing device for measuring the magnitude and direction of the motions of the movable bearings includes two piezoelectric gauges and a flexible vane having one end fast with the hub of one of said auxiliary bearings and the other end inserted between the two piezoelectric gauges rigidly connected to the support for said hub.

9. A machine as claimed in claim 1, in which the shaft of the assisted forming roll rotates in fixed bearings and the sensing device controlling the amplification chain of the assisting motor is associated to at least one deformable grip made fast, by means of a removable securing device, with the workpiece to be shaped, said sensor measuring the deformations of the grip responsively to the forces exerted on said workpiece through said grip.

10. A machine as claimed in claim 9, in which said grip is made up of two parts of unequal length separated by a gap and mounted on the device for attachment to said workpiece, the longer of these two parts being flexurally deformable.

11. A machine as claimed in claim 10, in which said sensing device includes a double-acting piezoelectric gauge which is inserted in a precompressed state into the gap between the two parts of said grip.

12. A machine as claimed in claim 10, in which said sensing device includes two strain gauges mounted on the longer part of the grip, proximate its end fast with the attachment device.

13. A machine as claimed in claim 9, in which one end of the grip is hingedly connected by first articulation means to the device for attachment to the workpiece and its other end is hingedly connected by second articulation means to a sensing device for measuring changes in the position of the grip relative to said attachment device in response to the urging forces applied to said grip and against springs tending to restore said grip into a neutral position.

14. A machine as claimed in claim 13, in which said sensing device includes a potentiometer placed inside the attachment device and having its slide mechanically connected to the grip by said second articulation means thereof.

15. A machine as claimed in claim 1, in which said motor is a hydraulic motor and said power amplifier is a hydraulic valve.

16. A machine as claimed in claim 1, in which said motor is an electric motor and said power amplifier is one of the group of components which includes electrical relays, magnetic amplifiers and electronic amplifiers.

17. A machine as claimed in claim 1, in which the signal delivered by said sensing device is an electric signal, that said differential amplifier is an electronic amplifier and that the input signal to the power amplifier is an electric signal. 

1. A shaping machine comprising two rotatable forming rolls with parallel axes between which items to be shaped such as sheet metal or panels are inserted and moved by a force external to the machine, said forming rolls being pressed against each other by a force which subjects the workpiece therebetween to a strain from which ensues a shaping thereof, at least one of said two forming rolls being mechanically connected to a motor associated with regulating means, said motor imparting to said forming roll a torque the magnitude of which is a direct function of the external force applied to the workpiece, said regulating means including an amplification chain comprising a power amplifier that energizes the motor as a function of the output signal from a differential amplfier across the inputs of which is connected a sensing device for measuring the magnitude And direction of the external force applied to the workpiece, shaping means in which a forming-roll shaft connected to said motor rotates in movable bearings which effect small displacements, the magnitude and direction of which are measured by the sensing device and as a result of which the forming-roll axis accompanies the motions of the workpiece in response to the external force, said bearings moving away in such cases from a resting position in which the plane containing the forming-roll axes is parallel to the direction of the force which presses said forming rolls against each other.
 2. A machine as claimed in claim 1, in which the slight motions of the movable bearings are rotations about an axis distinct from and parallel to the axis of the forming-roll supported by said movable bearings.
 3. A machine as claimed in claim 2, in which each movable bearing is eccentrically supported in a circular hub rotating in a fixed auxiliary bearing.
 4. A machine as claimed in claim 3, in which the fixed bearings are hydrostatic bearings.
 5. A machine as claimed in claim 4, in which each hydrostatic bearing comprises at least two supporting pockets separated by a rib which lies in the plane containing the forming-roll axes in said resting position.
 6. A machine as claimed in claim 5, in which the sensing device includes at least one pressure sensor associated to at least one of said supporting pockets whereby to measure the hydraulic pressure therein.
 7. A machine as claimed in claim 6, in which the differential amplifier in the amplification chain has its inputs connected to two pressure sensors of a hydrostatic bearing and applies to the power amplifier for energizing the motor a signal proportional to the pressure differential across the corresponding supporting pockets.
 8. A machine as claimed in claim 3, in which said auxiliary bearings are bearings with a fixed geometrical structure and the sensing device for measuring the magnitude and direction of the motions of the movable bearings includes two piezoelectric gauges and a flexible vane having one end fast with the hub of one of said auxiliary bearings and the other end inserted between the two piezoelectric gauges rigidly connected to the support for said hub.
 9. A machine as claimed in claim 1, in which the shaft of the assisted forming roll rotates in fixed bearings and the sensing device controlling the amplification chain of the assisting motor is associated to at least one deformable grip made fast, by means of a removable securing device, with the workpiece to be shaped, said sensor measuring the deformations of the grip responsively to the forces exerted on said workpiece through said grip.
 10. A machine as claimed in claim 9, in which said grip is made up of two parts of unequal length separated by a gap and mounted on the device for attachment to said workpiece, the longer of these two parts being flexurally deformable.
 11. A machine as claimed in claim 10, in which said sensing device includes a double-acting piezoelectric gauge which is inserted in a precompressed state into the gap between the two parts of said grip.
 12. A machine as claimed in claim 10, in which said sensing device includes two strain gauges mounted on the longer part of the grip, proximate its end fast with the attachment device.
 13. A machine as claimed in claim 9, in which one end of the grip is hingedly connected by first articulation means to the device for attachment to the workpiece and its other end is hingedly connected by second articulation means to a sensing device for measuring changes in the position of the grip relative to said attachment device in response to the urging forces applied to said grip and against springs tending to restore said grip into a neutral position.
 14. A machine as claimed in claim 13, in which said sensing device includes a potentiometer placed inside the attachment device and having its slide mechanically connected to the grip by said second articulation means thereOf.
 15. A machine as claimed in claim 1, in which said motor is a hydraulic motor and said power amplifier is a hydraulic valve.
 16. A machine as claimed in claim 1, in which said motor is an electric motor and said power amplifier is one of the group of components which includes electrical relays, magnetic amplifiers and electronic amplifiers.
 17. A machine as claimed in claim 1, in which the signal delivered by said sensing device is an electric signal, that said differential amplifier is an electronic amplifier and that the input signal to the power amplifier is an electric signal. 